Generally personal computers must pass a number of manufacturing tests after the system is built to ensure their quality.
One aspect that must be tested is the video output. At present, the video output is usually tested by having a human engineer connect a monitor to the system unit and inspect by eye an image generated by the system under test and displayed on the monitor. The efficiency of this method is low and suffers from being somewhat subjective in that each engineer has their own judgement and vision. Thus the testing can be inconsistent and inaccurate.
Various automatic systems have been proposed to try and improve this situation, but these have certain drawbacks and are not thought to have been widely adopted.
For instance U.S. Pat. No. 4894718 describes a video signal testing system in which a cyclic redundancy check circuit is connected to a expansion slot of the computer and the video output. A value measured from a video signal is compared with a fixed value to justify the correctness of the signals without the use of the human eye. This system suffers from the disadvantage that since the unit is connected to an expansion slot of the computer under test, the test must either be carried out before the unit is fully assembled, or the unit must be dismantled in order to effect the test.
U.S. Pat. No. 5537145 discloses a system in which the image display ed on the monitor is measured by an optical testing unit and the result fed back to the system via an I/O subsystem. As well as suffering from the disadvantages set out above of having to connect to an expansion slot in the computer, this system also suffers from an inability to distinguish between problems related to the monitor itself and the circuitry within the computer under test which generates the video signals.
This invention is directed to overcoming the problems of the prior art by providing a simple and relatively cheap arrangement for testing the video output of a computer.